Those who have irregular blood-glucose concentration levels are often medically required to self-monitor their blood-glucose concentration level. An irregular blood-glucose level can be brought on by a variety of reasons including illness, such as diabetes. The purpose of monitoring the blood-glucose level is to determine the concentration level and then to take corrective action, based upon whether the level is too high or too low, to bring the level back within a normal range. The failure to take corrective action can have serious medical implications.
Beyond the above-describe blood-glucose concentration level monitoring, self-testing systems are used for determining the presence or concentration of other analytes in body fluid such as, for example, cholesterol, alcohol, and hemoglobin in blood or chemical substances in saliva. Beyond self-testing situations, portable test devices are also used to test for various type of chemicals in water and soil.
One method of monitoring a person's blood glucose level is with a portable, hand-held blood glucose test device. A prior art blood-glucose test device 6 is illustrated in FIG. 1. The portable nature of these devices 6 enables the users to conveniently test their blood glucose-levels wherever the users may be. The test device 6 receives a test sensor 7 for harvesting the blood for analysis. The test sensor 7—one of which is required for each test—contains a reaction area including a regent for producing a measurable reaction with the glucose indicative of the blood-glucose concentration level. The test sensor harvests the blood, either prior to or subsequent to insertion into the testing device, for reaction with the reagent stored within.
The device 6 contains a switch 8a to activate the device 6 and a display 9 to display the blood-glucose analysis results. Alternatively, the device 6 is automatically activated upon receipt of the test sensor 7. In order to check the blood glucose level, a drop of blood is obtained from, for example, a lanced fingertip. The blood is harvested using the test sensor 7. The test sensor 7, which is inserted into a test device 6, is brought into contact with the blood drop. The test sensor 7 moves the blood to the inside of itself via, for example, capillary action. Alternatively, the a blood sample is harvested with the test sensor 7 prior to inserting the test sensor 7 into the test device. The blood sample now within the test sensor 7 mixed with the reagent causing a reaction between the reagent and the glucose in the blood sample. The test device 6, then measures the reaction to determine the concentration of glucose in the blood. Once the results of the test are displayed on the display 9 of the test device 6, the test sensor 7 is discarded. Each new test requires a new test sensor 7. There are different types of test sensors for use with different types of test devices. Electrochemical or optical (e.g., colorimetric) assays are two types of testing used to measure blood-glucose concentration levels.
During the manufacture of the reagents used within the test sensors or during the manufacture of the test sensors themselves, manufacturing variations occur from batch of test sensors to batch, also referred to as a “lot,” of test sensors that impact the performance of the test sensors or that impact the performance of the reagent in the test sensors. For electrochemical sensors, such variations within normal manufacturing tolerances include the size of the electrodes, the amount of reagent deposited within the sensor, the reactivity of the reagent (e.g., rate of dissolution and enzyme activity), and other sensor geometry variations. For optical sensors, manufacturing variations can include the reflectance of the sensor backing, absorbance level of the reagent, the amount of reagent deposited within the sensor, and transmittance of the sensor optics.
To correct for these variations, every package of test sensors is given a calibration number that corresponds to calibration adjustments stored in the testing device. The calibration adjustments inform the test device of how to adjust the obtained measurement for each particular batch of test sensors. Depending on the test device, there may be over 64 calibration algorithms and associated adjustments stored in the test device. Prior to each test, the user inputs the particular calibration number that corresponds to the correct calibration adjustment for the particular batch of test sensors currently being used for the analysis.
In many prior art devices, the test device 6 has a plurality of buttons 8b–e (FIG. 1) for inputting the calibration number into the test device. An increased number of buttons in the test device adds to the overall cost of the device and adds to the time to manufacture the device.
Other prior art test devices utilize a reading means such as a bar code scanner for reading the calibration number that has been bar coded on the package of test sensors. Other test sensors may be provided with a resistor that informs the test device, which must include an ohm meter for reading the resistor, of the calibration number. Both of these reading means add to the overall cost of the device. Further, the bar coded label can become torn or otherwise destroyed during shipping, making it unreadable, and the resistor can be damaged during shipping.
Other test devices utilize one button, which when pressed, causes the test device to scroll through all of the calibration numbers stored in the test device. While this minimizes the cost of production and the likelihood of breakdown, it is time consuming for the consumer to have to scroll through a plurality of numbers stored in the device, which, in turn, further increases the overall testing time.